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MPP LV6548 lower than expected PV power

lessthanspicoli

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Nov 26, 2021
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Hey all,
I have one MPP LV6548, currently with a string of 4x450w (50.5 Voc) panels in series. It is a very sunny day here, no cloud cover, but I am barely getting any input power. At the moment I am getting 184.6 V, but only 23 W of PV power and current is only sitting at 0.1 A.

I have tried switching between PV1 and PV2 inputs on the inverter, hoping that would isolate the problem, but getting similar readings. When I power cycle the invert, I do get 3-4 seconds of 600+ watts input, but then immediately drops back down to the 20-30 watts range. For some context, yesterday, which was very cloudy and overcast, I was also getting readings similar to today. I chalked those numbers up to cloud cover, but realizing today is as sunny as could be, my panels are at an appropriate angle for my lat/lon, and no shading at all, I would expect to see some more substantial power out of a "1800 watt" array.

I feel as if I'm doing something wrong in my setup, but not sure what. Any help would be greatly appreciated!
 
Are your batteries fully charged? That would explain low charging amps because the charger will only provide what the batteries require to obtain set voltage level. If they are fully charged, turn off the solar and power something with high draw (heater, hair dryer, etc) for a while, then turn the solar back on and see if charging amps go up.
 
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this ^^^

draw down the batteries to below your top charge voltage and put a 3000 watt load on it and report back....
 
Great call guys! That did it. Makes total sense as soon as you said it. Now I'm getting more like 700 watts.

I think I was expecting that metric to show what the maximum PV input could be, rather than showing draw based on need (current amps of load factored in).

Out of curiosity, is there any metric, or even way to calculate, what the total maximum PV input could be at any given time - regardless of load connected?
 
Glad it was that easy, I've "been there, done that" and had to pull a load to see what my PV charging could do. Your MPP manual (pull it off watts247.com if you weren't given one) will give you specs. Amps x charging voltage would be the max Watts your charger can output to charge the batteries. Likewise, there should be max ratings for input (don't go over max input voltage).
 
Great call guys! That did it. Makes total sense as soon as you said it. Now I'm getting more like 700 watts.

I think I was expecting that metric to show what the maximum PV input could be, rather than showing draw based on need (current amps of load factored in).

Out of curiosity, is there any metric, or even way to calculate, what the total maximum PV input could be at any given time - regardless of load connected?

I did the same thing... expected to see the "PV potential" not the "PV actual"....
 
Super helpful, thanks both! I'm sure I'll come back for more, but lesson learned and off to the races now!
 
Glad it was that easy, I've "been there, done that" and had to pull a load to see what my PV charging could do. Your MPP manual (pull it off watts247.com if you weren't given one) will give you specs. Amps x charging voltage would be the max Watts your charger can output to charge the batteries. Likewise, there should be max ratings for input (don't go over max input voltage).
Thanks in advance for any help ...

Just sent this note to MPP Solar support:

I just purchased two of your LV6548 modules and began working out the details of my configuration. I noticed that in your user's manual, it recommends a 6S2P configuration for each PV Input for a total of 24pcs for a total of 7920 Watts per inverter, with an Imp of 19.58 per PV Input. Yet, on page 42, in the Specs section, it states a "Max Input Current" of "18A x 2" in the Charge Mode Specification section. Does this mean that I cannot go over 18A per input from my PVs, even though I'm within the Wattage limits? Or does this mean that this is the max that will be sent to the batteries?

From your comment above, I'd guess the second option is correct, that that's what's sent to the batteries?
 
I'll first admit I don't have first-hand experience with this (over paneling), but my understanding is the MPP will only use 18A per input even if it's receiving more. So my take is your second option is correct. May not be important since panels will typically produce less than full amps they're capable of producing in ideal conditions.

The rating of 18 Amps is on PV input; but I don't see a max charger output rating listed under PV although it lists 120 Amp max for utility charging. I wouldn't be surprised if MPP responds that 120 Amp output also applies regardless of input source (utility or PV).
 
See post #166. The VOC is the one you have to watch out for.
The load will pull the current from panels, panels do not push current.

  1. 120A Mppt at max 250Voc – 2 x ( 4kW MPPT Charge Controllers)
  2. 120A Utility Charger (120A at 48V = 5.7kW or 48A at 120V)
 
PV input 24 ~ 28A each according to the video @1:25 per Ian from WATTS247
 
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Did you get a response from their support?
Yes ... and sorry for not posting here ... I think I did post the response on another similar thread ...

From Andy Y. at MPP Solar to Jason at Santan Solar (who I had cc'd): "Please don't worry. PV input current 22A is ok and it will not cause the unit damage. We suggest that please keep the max PV input current within 25A. Thank you."

So, it clips at 18A, safe to 25A. Important limitation is the voltage. Also, if you have the MPP LV6548's, go get the Phocos PSW-H-6.5kW-120/48V instruction manual ... it's FAR more robust than MPP's instruction manual and it's the identical box except that the Phocos has the ability to push back onto the grid.
 
My panels are 395W / 49.03VOC, so I am assuming I can 5S = 245.15V into a LV6548.
However, I asked this question of Ian at Watts247, and he said.
5s is pushing it, maybe if you lived in the Bahamas.
Voltage rises when temps cool.
4s2p is better. A little less, but you have lots of inputs on these units.
4 inputs in total that's 32 panels ( 4 x 8 panels 4s2p)
I was under the impression that VOC was max in perfect conditions and that's not likely.
Is there a down side to getting close to 250V max or an upside to staying ~200V well below the unit limit?
 
My panels are 395W / 49.03VOC, so I am assuming I can 5S = 245.15V into a LV6548.
However, I asked this question of Ian at Watts247, and he said.

I was under the impression that VOC was max in perfect conditions and that's not likely.
Is there a down side to getting close to 250V max or an upside to staying ~200V well below the unit limit?
You're limited by your min and max temperature spread for wherever you live ... go look at the below for your panels, then go find the lowest temp ever for your area, then be reasonable as to how often that might happen to design your system. 245V not likely possible, and there was another guy on here who was having trouble with his boxes somewhere near that voltage. I'm personally running mine at 164V NMOT (20 C). I looked up the coldest day ever in Austin and determined that at that temp my panels would have a voltage of around 220V ... so I was good.

And, the tradeoff is ... the higher the voltage, the less amps needed to deliver the same amount of power, and thus smaller wire sizes will be needed, saving $$. So design your system at the highest voltage possible at the lowest ambient temp for your area that you think is reasonable.
1644511211144.png
 
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And, the tradeoff is ... the higher the voltage, the less amps needed to deliver the same amount of power, and thus smaller wire sizes will be needed, saving $$. So design your system at the highest voltage possible at the lowest ambient temp for your area that you think is reasonable.
Thank you. I'm NE of Tyler, TX, so other than last year really cold might be a daytime low of 10f air temp, but irradiated panels would likely be warmer due to sunlight absorption....correct?

My panels are 49.03VOC @ 25C with VOC Temp @ -.3%/C, so if I make it to -15C that would be:
40 * .3% = 12% low temp voltage gain = 54.91V at low temp. X5 puts me well over the 250V max.
Is this roughly the correct way to evaluate this?
 
Thank you. I'm NE of Tyler, TX, so other than last year really cold might be a daytime low of 10f air temp, but irradiated panels would likely be warmer due to sunlight absorption....correct?

My panels are 49.03VOC @ 25C with VOC Temp @ -.3%/C, so if I make it to -15C that would be:
40 * .3% = 12% low temp voltage gain = 54.91V at low temp. X5 puts me well over the 250V max.
Is this roughly the correct way to evaluate this?

Try this calculator as a cross-check:
 
Thank you. I'm NE of Tyler, TX, so other than last year really cold might be a daytime low of 10f air temp, but irradiated panels would likely be warmer due to sunlight absorption....correct?

My panels are 49.03VOC @ 25C with VOC Temp @ -.3%/C, so if I make it to -15C that would be:
40 * .3% = 12% low temp voltage gain = 54.91V at low temp. X5 puts me well over the 250V max.
Is this roughly the correct way to evaluate this?
Yep, looks correct. If your whole system is 5 panels, suggest you buy one more panel, go to 2P3S ... putting you well in range of everything, and you'll likely be buying 8AWG instead of 10AWG wire once you combine the Series ...
 
Yep, looks correct. If your whole system is 5 panels, suggest you buy one more panel, go to 2P3S ... putting you well in range of everything, and you'll likely be buying 8AWG instead of 10AWG wire once you combine the Series ...
I've got 32 panels. The new plan is 4 x 4S2P arrays = 12.64KW.
I've got a lot of 10AWG PV wire with a 100' run, so I hope that will work without much loss @ 18-19.4A max.
 
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